LONDON — As fighting continues in Syria between government and opposition forces, there are growing concerns that Islamist fighters, including some foreigners linked to terror groups like al-Qaida, are joining up with the Free Syria Army. At least one expert says there's ample online and video evidence that the Syrian uprising is being exploited by Jihadist groups.

Free Syria Army fighters on the outskirts of Aleppo earlier this month. As Western and Gulf powers step up their aid for the Syrian opposition, concerns are growing that Islamist militant groups are infiltrating the conflict.

Shiraz Maher of the International Centre for the Study of Radicalization, at Kings College, London, specializes in monitoring extremist groups. He took VOA through some of the videos and websites he'd tracked down online. This one purports to show bombing operations carried out by al Qaida in Syria.

"Certainly groups that are Islamist in orientation, whether they're affiliated with al-Qaida or not, are now operating on the ground there. Videos like this, of course are very difficult to independently verify but we can cross reference them with other things that we're seeing. These videos are now surfacing through known al-Qaida web forums that we've been following for the best part of a decade now," he said.

Iconography associated with Islamist militant groups is becoming increasingly common in videos purportedly shot in Syria.

"They say it's al-Qaida, it's certainly Islamist fighters within Syria. You can tell that from the flags that they're carrying and also from some of the iconography put onto the video. What they're doing is that they're transporting rugs here and blankets into a rebel-held area. This is typical of the way that Islamist groups in the region operate, in order to win over support from local populations," he said.

In recent weeks, there have been several reports in the Arab press of foreign fighters going to join the Free Syria Army. Maher says it is impossible to know for sure the numbers of foreigners among the FSA ranks, but they are certainly present.

"Saudis for example going, Egyptians, Libyans, Jordanians. And of course that would tend to make sense. These are, particularly in the Gulf states, regimes that have expressed opposition to Bashar al Assad. Many of the clerics in those countries have declared Bashar al Assad an apostate," he said.

Maher says that extremist groups were slow to react to the Syrian uprising, but in recent months, there are increasing signs that militant Islamist networks are looking to exploit the conflict.